Design
Street
Urban
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Urban Street
Design Guide
i v Terry Bellamy Director,
The National Association of City Transpor-tation Officials is a 501(c)(3) nonprofit association that represents large cities on transportation issues of local, regional, and national significance. NACTO views the transportation departments of major cities as effective and necessary partners in regional and national transportation efforts and promotes their interests in federal decision making. The organization facil-itates the exchange of transportation ideas, insights, and best practices among large cities, while fostering a cooperative approach to key issues facing cities and metropolitan areas. As a coalition of city transportation departments, NACTO is committed to raising the state of practice for street design and transpor tation by building a common vision, sharing data, peer-to-peer exchange in workshops and conferences, and regular communication among member cities.
NACTO Board of Directors: New York, NY Edward D. Reiskin NACTO Vice President Director of Transportation, Municipal Transportation Agency Richard Mendoza Commissioner,
Department of Public Works
Baltimore, MD William M. Johnson Director
Deputy Director of Public Works, Public Works and Engineering Department
Los Angeles, CA Jaime de la Vega General Manager,
Department of Transportation
Minneapolis, MN Jon Wertjes
Director of Traffic & Parking Services, Department of Public Works
Philadelphia, PA Rina Cutler Deputy Mayor,
Mayor’s Office of Transportation and Utilities
National Association of City Transportation Officials 55 Water Street, 9th Floor New York, NY 10041 www.nacto.org
Cataloging information may be obtained from the Library of Congress.
Library of Congress Control Number: 2013946303
ISBN: 978-1-61091-494-9
© Copyright 2013 National Association of City Transportation Officials
Consultant Team: Nelson\Nygaard Consulting Associates, Sherwood Engineers
Design: Pure+Applied
Web: BlinkTag
Acknowledgments
CO N T E N T S
3 Street Design Principles
4 Key Principles
45 Curb Extensions 47 Gateway 48 Pinchpoint
49 Chicane 50 Bus Bulbs
51 Vertical Speed Control Elements 53 Speed Hump
54 Speed Table 55 Speed Cushion
57 Transit Streets
58 Dedicated Curbside/Offset Bus Lanes
60 Dedicated Median Bus Lanes 61 Contra-Flow Bus Lanes 62 Bus Stops
65 Stormwater Management
67 Bioswales
68 Flow-Through Planters 69 Pervious Strips 70 Pervious Pavement
Interim Design Strategies
73 Interim Design Strategies
74 Moving the Curb 76 From Pilot to Permanent
77 Parklets
80 San Francisco Parklet Program
81 Temporary Street Closures
84 Los Angeles’s CicLAvia Initiative
85 Interim Public Plazas
88 New York City Plaza Program
Intersections
91 Intersection Design Principles 92 Principles
94 Major Intersections
96 Intersections of Major and Minor Streets 98 Raised Intersections
v i
Intersection Design Elements
109 Crosswalks and Crossings 110 Crosswalks
112 Conventional Crosswalks
114 Midblock Crosswalks 116 Pedestrian Safety Islands
117 Corner Radii
121 Visibility/Sight Distance
125 Traffic Signals
126 Signalization Principles 128 Leading Pedestrian Interval 129 Split-Phasing
130 Signal Cycle Lengths
132 Fixed vs. Actuated Signalization 134 Coordinated Signal Timing
Design Controls
137 Design Controls
139 Design Speed
142 Speed Reduction Mechanisms
143 Design Vehicle
147 Design Hour
151 Design Year
155 Performance Measures
159 Functional Classification
162 San Francisco’s Better Streets Plan
Resources
165 Notes
174 References
F O R E WO R D
This design guide is part of a growing movement among
cities, from New York to San Francisco, and from Chicago
to Houston. Together, we’re working to build sustainable
streets that will carry us into the 21st Century and create a
new DNA for city streets.
As president of the National Association of City
Transportation Officials (NACTO), I’ve led a group of cities
engaged in creating this new set of standards for city streets.
In 2011, we released the first edition of the Urban Bikeway
Design Guide, and now we’re releasing the Urban Street
Design Guide with a much broader scope. The impulse to
write a new guidebook started in individual cities, with over
ten major guides written over the last few years, tailored
to those individual cities. In New York City, we released
a new Street Design Manual in 2009. These publications
are already changing the game, pulling away from a
Foreword
Janette Sadik-Khan
NACTO President
v i i i
The Urban Street Design Guide gives an overview of the
principles that cities are using to make their streets safe and
inviting for people walking, shopping, parking, and driving in
an urban context. These principles are about creating real
spaces for people on city streets. Economic development is
integrally tied into this transformation, since great streets
support city businesses. And paramount to all of this is the
safety of people, old and young, on our city streets.
Still, transformation can take time, and can be difficult in the
built environment of a city. New York City and others have
been leading the way to making these changes through a
new, faster implementation process. Improvements that use
low-cost materials like planters, bollards, and markings can
bring enormous benefits in a short period of time. In this
guide, for the first time, the recipes for doing these quick
implementation projects are laid out for the cities around the
country and the world who are clamoring for it.
Over the coming century, the challenges borne by cities
and the burdens placed upon their streets will multiply in
quantity and complexity. Growing urban populations will
demand that their streets serve not only as corridors for
the conveyance of people, goods, and services, but as
front yards, parks, playgrounds, and public spaces. Streets
must accommodate an ever-expanding set of needs. They
must be safe, sustainable, resilient, multi-modal, and
economically beneficial, all while accommodating traffic.
In response to these unprecedented demands, cities
around the country are developing an innovative body of
practice and expertise to design for and around the special
characteristics of the urban environment. From New York’s
Times Square to Chicago’s Wacker Drive to Spring Street
in Los Angeles, a better approach to and understanding of
street design is taking root in our cities.
x
Using the Guide
The contents of this guide have been formatted so that a reader may engage with the material in a non-linear fashion. While each section provides varying degrees of detail and information, these sections present individual topics which do not require a complete reading of the material that precedes it.
REL ATION TO OTHER
NATIONAL , STATE, AND LOCAL DESIGN GUIDELINES
The Urban Street Design Guide focuses on the design of city streets and public spaces. While other national manuals, such as AASHTO’s A Policy on Geometric Design of Highways and Streets, provide a general discussion of street design in an urban context, the Urban Street Design Guide empha-sizes city street design as a unique practice with its own set of design goals, parameters, and tools.
In instances where a particular sign or marking should be used, the guide highlights its specific reference to the Manual for Uniform Traffic Control Devices (MUTCD).
Many cities have already gone through the process of developing a local street design manual in the interest of creating internal design consensus between different local agencies. NACTO references materials from a selection of these guides and urges municipalities to use the Urban Street Design Guide as a basis for the creation of local standards.
It is important to note that urban situations are complex. The treatments and topics discussed in this guide must be tailored to individual situations and contexts. NACTO encourages good engineering judgment in all cases. Decisions should be thoroughly documented. To assist with this, this guide links to references and cites relevant materials and studies.
Certain sections of the guide reference material in its companion document, the Urban Bikeway Design Guide (2nd edition), which may be accessed online at c4cguide.org.
For most topics and treatments in this guide, the reader will find three levels of guidance.
Critical Features are elements for which there is a strong consensus of absolute necessity.
Recommended Features are elements for which there is a strong consensus of added value.
Optional Features are elements that may vary across cities and may add value, depending on the situation.
Note: Certain sections contain a general discussion only and have no critical, recommended, or optional points.
(above) Key points on renderings are highlighted in yellow. Highlights either refer to the treatment or topic being discussed or to the main thrust of the image shown.
Streets
3 Street Design Principles
4 Key Principles
6 Phases of Transformation 7 Street Design in Context 8 Downtown 1-Way Street 10 Downtown 2-Way Street
12 Downtown Thoroughfare
14 Neighborhood Main Street
16 Neighborhood Street
17 Yield Street 18 Boulevard
20 Residential Boulevard 22 Transit Corridor 24 Green Alley
25 Commercial Alley
26 Residential Shared Street 28 Commercial Shared Street
Street Design
Principles
4
Key Principles
KE Y PRIN CIPL E S
Streets Are Public Spaces Streets are often the most vital yet underutilized public spaces in cities. In addition to providing space for travel, streets play a big role in the public life of cities and communities and should be designed as public spaces as well as channels for movement.
Great Streets are Great for Businesses
Cities have realized that streets are an economic asset as much as a functional element. Well-designed streets generate higher revenues for businesses and higher values for homeowners.1
Streets Are Ecosystems Streets should be designed as ecosystems where man-made systems interface with natural systems. From pervious pavements and bioswales that manage storm-water run-off to street trees that provide shade and are critical to the health of cities, ecology has the Design for Safety
In 2012 in the U.S., over 34,000 people were killed in traffic crashes, which were also the leading cause of death among children aged 5–14. These deaths and hundreds of thousands of injuries are avoidable. Traffic engineers can and should do better, by designing streets where people walking, parking,
Streets Can Be Changed
Transportation engineers can work flexibly within the building envelope of a street. This includes moving curbs, changing alignments, daylighting corners, and redirecting traffic where necessary. Many city streets were built or altered in a different era and need to be reconfigured to meet new needs. Street space can also be reused for different purposes, such as parklets, bike share, and traffic calming.
Act Now!
6
Existing
Existing conditions demonstrate how traditional design elements, such as wide travel lanes and undifferentiated street space, have had an adverse impact on how people experience the streetscape.
Phases of
Transformation
The streets shown in this guide are depicted in three stages of transformation: existing, interim, and reconstruction.
Interim design changes for streets can be carried out using low-cost materials. These interim design strategies realize the benefits of
a full reconstruction in the short term, and can help build support for projects or test their consequences. While not all projects should or need to go through these three phases, many projects can benefit from this approach.
Interim Redesign
Striping and low-cost materials can realize the benefits of a full reconstruction in the short term, while allowing a city to test and adjust a proposed redesign.
Reconstruction
S T R E E T D E SI G N IN CO N T E X T
Street Design
in Context
Context is a crucial, yet often overlooked, parameter in designing streets. Street design should both respond to and influence the desired character of the public realm.
Rooted in city goals and policies, designers can work to enhance their surroundings by fulfilling the visions and desires of adjacent communities through street design.
Commercial Strip
A single corridor can pass through multiple environments within the city, each with a different character and usage pattern. At right, a roadway passes through an auto-oriented commercial zone but has the same right-of-way as the two streets below.
Residential Boulevard The same right-of-way serves a different purpose as it passes through a residential area. In this environ ment, the street can be used for plantings, on-street parking, and shaded sidewalks.
Downtown Street
8
EXISTING CONDITIONS
The existing conditions shown in the illustration above are typical of many city streets in the downtown core. Many of these streets have been designed for a 15-minute peak period and remain well below capacity at other times of day.
1 Undifferentiated street space and wide travel lanes can result in higher speeds and are an ineffective use of valuable street space.
Many downtown 1-way streets have travel lanes with extra capacity or peak-hour restricted parking lanes.
Bicyclists feel uncomfortable riding between fast-moving traffic and the door zone. Double-parked vehicles may cause bicyclists to weave into traffic unpredictably, creating unsafe conditions for both motorists and bicyclists.
RECOMMENDATIONS
2 On downtown streets with heavy bus traffic, a red bus-only lane may be applied at curbside or offset. Bus-only lanes require significant enforcement and may be encroached upon by double parked cars and loading vehicles without proper enforcement. Combine bus-only lanes with bus bulbs, shelters, and transit signal priority to increase their effectiveness.
Analyze existing traffic volumes to determine whether or not peak-hour lanes can be removed and converted to on-street parking, bus or bike lanes, or additional sidewalk space. Converting underutilized travel lanes to other uses can eliminate potential conflicts within the roadway and improve traffic operations. In the mid-20th century, many 2-way
downtown streets were converted to 1-way operation to streamline traffic operations, reduce conflicts, and create direct access points to newly built urban freeways. Today, many of these streets operate significantly below capacity and create swaths of empty pavement in downtown areas. While many cities are convert ing these streets back to 2-way operation, these broad roadways can be narrowed using cycle tracks and transit lanes, which require less cost and analysis, and optimize usage of the street as a public space.
Existing
Downtown 1-Way Street
D OW N T OW N 1 -WAY S T R E E T
3 A raised cycle track or parking-buffered cycle track applied on the left side of a 1-way street, removes cyclists from potential conflicts with bus traffic and creates a pedestrian safety island that decreases exposure time for pedestrians. Note: 2-way cycle tracks can also function effectively on 1-way streets in some instances. Where 2-way cycle tracks are installed, consider mitigating contra-flow turn conflicts by using bicycle signals, turn restrictions, and other means that improve visibility and slow motorists turning at the intersection.
4 As part of a full reconstruction, consider widening sidewalks, especially when they have previously been narrowed in favor of additional travel lanes.
The street illustrated above depicts a 46-foot roadway within an 86-foot right-of-way.
NEW YORK, NY
In 2010, 1st Avenue in New York City was redesigned with a 1-way cycle track, Select Bus Service, and pedestrian safety islands. The redesign not only carved out room for bicyclists, but shortened long, unsafe crossings for pedestrians. The avenue has since become a model for the successful transformation of the city’s major avenues. 2
3
4
10
EXISTING CONDITIONS
The above illustration depicts a constrained 2-way street in a central business district. While many down-town streets were converted to 1-way operations, many were not, resulting in streets that are heavily congested by buses, bikes, people, and cars. Especially in older cities, these streets may be a main route for multiple modes.
1 On major bus routes, curbside bus stops may be undermined by double-parked vehicles and heavy rush-hour traffic. These obstructions hurt the reliability and on-time performance of transit vehicles.
A lack of organization and striping can invite unintended uses and double-parking.
Freight vehicles double-parking at peak hours create weaving conflicts and safety hazards for motorists and bicyclists.
Busy downtown 2-way streets are often the most difficult streets for cities to recon figure and retrofit. Many of these streets suffer from double parking and loading conflicts, have heavy turn volumes, and offer insufficient accommodations for bicyclists and pedestrians. Retrofit constrained 2-way streets using lane diets and conventional bike lanes or add cycle tracks that decrease the overall width and offer a higher quality bicycle facility.
Downtown 2-Way Street
CHICAGO, IL
SAN FRANCISCO, CA
1
D OW N T OW N 2-WAY S T R E E T
RECOMMENDATIONS
2 Bus bulbs serve as dedicated waiting areas for transit users while decreasing pedestrian exposure during crossings. Far-side placement is preferable to near-side when possible. Apply turn restrictions for near-side bus bulbs where right-turning vehicles are likely to queue in the right lane. Bus bulbs may be created in the near term without affecting drainage if slightly offset from the curb or designed as a bus-boarding island with a bicycle cut-through.
3 Create definition in the roadway using striping, cycle tracks, and narrow travel lanes.
2
3 4
SEAT TLE , WA
This street in Seattle uses a planted central median to create a street geared towards slower speeds.
4 Cycle tracks require special attention at intersection crossings. Conflicts should be high-lighted using intersection crossing markings with the application of color optional. Bicycle signals may need to be applied for bicycle traffic to operate safely along the corridor, though bikes may use pedestrian signals in an interim design. Turning conflicts may be reduced through the implementation of turn restrictions.
5 Restricting freight delivery or encouraging off-peak freight delivery is critical to eliminating double-parking obstructions. Off-peak deliveries are faster and more cost-efficient and avoid obstruction of the bike lane or delays to buses and local traffic. At peak loading times, dedicated loading zones should be provided to avoid the need for freight vehicles to double-park. Designers may also consider the use of wide parking lanes in these situations.1
5
12
RECOMMENDATIONS
1 Assess left-turn volumes and evaluate the overall traffic net-work to determine whether or not left turns can be restricted or removed at a particular intersection. Where left turns must be retained, consider split-phasing options that provide a dedicated left-turn phase.
2 A parking-buffered 1-way cycle track, applied on each side of the street, offers a high-quality experience to bicyclists.
3 The cycle track may also be combined with an offset bus-boarding island and other amenities that improve operations for pedestrians and transit users. Major streets that connect
neigh-borhood centers or run through the downtown can be daunting for pedestrians to cross, depressing property values and the quality of the public realm as a result. While many of these streets have significant traffic volumes at peak hours and bustle with activity throughout the day, there are opportunities to improve these corridors for every one using them. Add a central median and cycle tracks to enhance the experience of the street and to reduce its overall width.
EXISTING CONDITIONS
The illustration above depicts a major 2-way downtown arterial with 6–8 lanes of traffic. This street runs directly through the heart of the city and is a major connector to other neighborhoods. The street has heavy turn volumes and multiple signal phases, making it a barrier for people to cross.
Left turns are a frequent source of conflict between motorists and pedestrians and a common cause of head-on collisions.
Buses experience frequent delay due to the encroachment of parked cars, loading freight vehicles, and through traffic. Bicyclists lack any accommodation on the street whatsoever, forcing many to utilize the sidewalk as an alternative.
Downtown Thoroughfare
D OW N T OW N T H O R O U G H FA R E
BROOKLYN, NY
Striping and left-turn pocket closures provide a better pedestrian safety area. 2
3
4 At intersections, 1-way cycle tracks may either mix with right-turning vehicles in a “mixing zone,” or, where turn volumes compromise bicyclist comfort and safety, be given a dedicated bicycle phase.
As an alternative to the treatment shown above, a 6-foot pedestrian safety island and dedicated left-turn bay may be retained at the intersection by tapering the bike lane buffer and shifting the rightmost travel lane.
Many major urban arterials with commercial strip development may be reconfigured using the same principles as described above. In such cases, land use changes and access management should be coordinated with the overall vision and redesign of the street.
The street illustrated above depicts an 84-foot roadway within a 114-84-foot right-of-way.
4
1
14
EXISTING CONDITIONS
The illustration above depicts a main street with 4 lanes of traffic. With medium traffic volumes and high pedestrian activity, the street has significant potential for regeneration as a retail district, yet currently under-performs for those who shop, eat, and walk there. Frequent destinations have resulted in multiple turning and weaving conflicts along the street.
1 4-lane configurations have been shown to increase rear-end and sideswipe vehicle crashes and pose a higher pedestrian crash risk.1
RECOMMENDATIONS
While road diets are not appropriate on all 4-lane cross sections, streets carrying up to 25,000 vehicles per day function effectively with 3 lanes, depending on the traffic volumes of nearby adjacent streets.2
The weaving line in the 4-lane configuration shows the pattern of a driver avoiding double-parked vehicles and drivers turning left and right.
In a 3-lane configuration, the weaving and conflicts are eliminated.
Neighborhood main streets are a nexus of neighborhood life, with high pedestrian volumes, frequent parking turnover, key transit routes, and bicyclists all vying for limited space. Main-street design should limit traffic speeds and create a narrower profile with frequent, high-quality pedestrian crossings. In recent years, many main streets have been significantly improved through road diets and the conversion from 4 to 3 (or 6 to 5) lanes of travel with bike lanes and a center turning lane or median.
Neighborhood Main Street
1
N E I G H B O R H O O D M A IN S T R E E T
5
4 3
Road diets can improve traffic flow and reduce conflicts with turning vehicles, while increasing a road’s efficiency by channeling turning vehicles out of the through lanes.Streets designed with either 2 lanes or a 2-way left-turn lane can cut crash risk by nearly half.3
Implementation of a road diet should consider the availability of parallel routes, the potential for mode shift, and the channelization of traffic using additional signals.
2 Turn lanes can help to eliminate weaving conflicts on 4-lane roads. As an alternative to the illus-tration above, a 6-foot pedestrian safety island can be retained in the above configuration by tapering the bike lane buffer near the inter-section and shifting the through lanes to the right.
3 The application of a road diet may be carried out in two phases, the first consisting solely of striping
2
4 From an economic standpoint, road diets often rank favorably with business owners and have a pos-itive impact on local business activity.4
5 Bike boxes help cyclists make left or right turns by placing them in front of traffic at a red light. On streets with higher traffic volumes, cyclists may choose to make a two-stage turn.
6 Parklets are ideal for neighbor-hood main streets with active storefronts, heavy foot traffic, and lots of retail activity.
7 Streets with both heavy freight and parking demand, as well as on-street bike lanes, benefit from dedicated loading zones near the intersection. Loading zones help reduce obstruction of the bike lane and make deliveries easier for businesses. Loading zones can be striped and signed, or managed for off-peak deliveries.
6
7
BROOKLYN, NY
16
RECOMMENDATIONS
1 On 1-way neighborhood streets, travel lanes may be striped to narrow the percieved width of the roadway. An undifferentiated traveled way encourages higher speeds. Crash rates have been shown to increase as lane width increases.
2 Left-side bike lanes reduce the risk of dooring conflicts and are an effective treatment for most neighborhood streets.
3 Raised crosswalks or curb extensions maintain safe travel speeds and reinforce the residential nature of the street.1
The street illustrated above depicts a 30-foot roadway within a 50-foot right-of-way.
Neighborhood
Street
CAMBRIDGE , MA
Bike lanes narrow this residential street and serve as a valuable low-volume route for commuters.
1
2
3 Local streets in residential
Y IE L D S T R E E T
Yield Street
RECOMMENDATIONS
For a yield street to function effec-tively, motorists should be able to use the street intuitively without risk of head-on collision. Depending on whether the yield street has high or low parking utilization, flush curbs, or other features, its configuration may vary. A yield street with parking on both sides functions most effectively at 24–28 feet, while yield streets with parking on only one side can be as narow as 16 feet.1
1 All residential streets should provide safe and inviting places to walk and good access to local stores and schools. Design should mitigate the effects of driveway conflicts, reduce cut-through traffic, and maintain slow speeds conducive to traffic safety.
1 2
3
PORTL AND, OR
A curb extension narrows the entry and slows turning vehicles at the mouth of this yield street.
2-way yield streets are appro- priate in residential environments where drivers are expected to travel at low speeds. Many yield streets have significant off-street parking provisions and on-street parking utilization of 40–60% or less. Create a “checkered” parking scheme to improve the function-ality of a yield street.
2 Driveways should be constructed to minimize intrusion upon the sidewalk. Maintain sidewalk materials and grade across driveways.
3 The planted furniture zone of the sidewalk creates opportunities for street trees, bioswales, pervious strips, and rain gardens.
4 While most yield streets should have a minimum of signage and striping, signage should be used to indicate bidirectional traffic at transition points or where 2-way oper-ation has recently been introduced.
Parking utilization on yield streets should be monitored closely. Before and after conversion, cities should consult with local residents to see whether or not a “checkered” parking scheme should be striped or remain unofficial.
The street illustrated above depicts a 30-foot roadway within a 45-foot right-of-way.
18
RECOMMENDATIONS
1 The frontage road, especially in a residential context, benefits from traffic calming at intersections and midblock as well as pedestrian-scale lighting and street trees. These enhancements preserve safe speeds for bicyclists and pedestrians, and encourage recreational and commercial activity.
2 Boulevards require careful attention at intersections with cross traffic. Poor design can result in intersections that are confusing or unsafe for all street users. In general, frontage roads should be stop-controlled, except in cases where volumes of cross traffic fail to provide sufficient gaps to pass. In such cases, require vehicles on the frontage road to turn or install a signal in conjunction with the through lanes.1
3 Boulevard medians are often under-designed or inhospitable as public space. Intersection conflicts and delays undermine their use. Medians can be activated through the addition of shared use paths, seating, and recreational amenities. Consider the installation of curb extensions or midblock crossings to facilitate median use and access, or design the frontage road with a flush curb to create a seamless transition between the sidewalk, street, and median.
Transit providers may prefer to use the frontage road over the throughway to reduce risks of rear-end collisions and provide more direct access to adjacent homes and businesses. When used as a transit route, the frontage road should be designed with curb extensions and/or speed cushions and should be signalized to ensure the effectiveness of transit service.
BERKELEY, CA
Frontage roads create a parallel low-speed urban environment ideal for retail activity.
SAN FRANCISCO, CA
Low-speed, low-volume frontage roads are shared by multiple users.
1
3 Boulevards separate very large
streets into parallel urban realms, buffering the commercial or res-idential street edge from the high-speed throughway by means of multiway operations and frontage roads. Many boulevards were built at the turn of the 20th century, but fell into disrepair or were redesigned to highway standards over the course of the century. Today, many cities are restoring these boulevards to their former grandeur or applying updated boulevard design stan-dards to overbuilt urban arterials.
B O U L E VA R D
5 A boulevard median with a shared use path should be designed with careful attention to intersection crossings and turning conflicts. Use access management strategies and turn requirements to eliminate these conflicts and ensure that potential intersection conflicts are well marked and highly visible to motorists turning off the throughway as well as to cross traffic.
The street illustrated above depicts a 116-foot roadway within a 164-foot right-of-way.
4 Frontage roads provide additional parking to local businesses and residents. Back-in angled parking may be an option if space is available.
Boulevards may benefit from access management strategies. At local or low-volume intersections, consider creating a T-intersection by extending the median and forcing turns. Through traffic and recreational median users both benefit from this configuration. Midblock pedestrian crossings should still be provided to preserve crossing opportunities.
PHIL ADELPHIA , PA
Rows of trees make walking pleasant and provide shade in summer.
4 5
20
EXISTING CONDITIONS
The illustration above depicts a broad residential thoroughfare in an older neighborhood. The central median is underutilized. While traffic volumes may not be high, speeds are, creating highway-like conditions in a predom-inantly residential area.
1 Many historic central medians are underused and lack recreational space. High speed crossings make it difficult for residents and children to safely access the median.
While parkways and boulevards provide natural links in an active trans-portation network, many lack safe and adequate paths for recreational use.
Parking demand and utilization may vary depending on the amount of off-street parking available to residents. Broad historic boulevards and
parkways often function as high-speed thoroughfares, even though their adjacent land uses may be primarily residential in nature. In many cases, these streets have excess width, underutilized on-street parking, and too many travel lanes. Retrofit residential boulevards by expanding or activating the median, adding curbside or left-side bike lanes, and curb extensions that provide direct access from homes to the center median.
BOSTON, MA
Commonwealth Avenue has a linear park in its median.
NEW YORK, NY
A cycle track takes advantage of the central median and insulates cyclists from double parking.
Residential Boulevard
1
R E SID E N T IA L B O U L E VA R D
RECOMMENDATIONS
2 Activate the central median with plantings, street trees, walkways, and seating. Broad central medians can become a community focal point as well as an active space for recreation, exercise, and leisure. Provide curb extensions and/or midblock crossings to make it safer and easier for residents to access the median.
3 A raised cycle track takes advan-tage of the central right-of-way, avoids frequent conflicts with drive-ways and double-parked cars, and effectively expands the amount of recreational space along the corridor.1
ST. LOUIS, MO
Many historic neighborhoods have medians with untapped civic potential.
2
3 4
2 2
RECOMMENDATIONS
1 Transit corridor retrofits should be coordinated with land use changes to maximize a corridor’s potential for economic growth and physical transformation. Setback guidelines and other land use regu-lations should be tailored to create a pedestrian-scale environment.1 Transit corridors, including light rail (LRT), streetcar, and bus rapid transit (BRT), promote economic development around high-quality transit service while fostering a pedestrian scale in which walking and biking actively complement public transit. As major generators of pedestrian traffic, heavy surface transit routes should be prioritized for pedestrian safety improvements in both the immediate surrounding area and major access routes within the transit access shed. When redesigning streets for high-quality transit service, designers should assess how transit service is impacted not only by the geometry of the corridor, but also its existing signal timing, signal phasing, turns, and other operations that may jeopardize the quality of service.
2 A raised cycle track on both sides of the corridor promotes the combination of bicycle and transit usage. A center-running 1-way or 2-way cycle track may be preferable in some cases to reduce the dangers of turning conflicts in combination with transit.
Enforcement measures should be put in place to discourage encroaching vehicles from using the dedicated bus lanes. In some cases, median transit lanes may serve as a route for emergency vehicles.
3 Corridors with high transit traffic, where double-parking and local traffic pose obstacles to effective transit, should be considered for BRT, LRT, or streetcar. High-quality transit service and median transit lanes decrease conflicts between buses and through traffic on heavy transit routes, can speed travel times, and reinforce the desirability of transit as an option.2
Wide transit corridors are challenging to cross in a single cycle. Consider the tradeoffs between shortening signal cycle lengths and providing sufficient time for all pedestrians to cross the street.
4 Off-board fare collection speeds up transit vehicles and reduces wait time for passengers.
Transit signal priority gives buses and light rail more green time and should always be used as part of BRT or LRT operations.3
2
T R A N SIT CO R RID O R
A side-running bus, streetcar, or light rail system may be preferable when adjacent land uses are heavily weighted toward one side of the corridor.
5 The design of a transit stop is an opportunity to reinforce the speed and desirability of the system. Shelters and stations should be built to accommodate the typical number of waiting passengers at the peak hour.
Loading zones should be provided near the intersection in the floating parking lane to discourage double parking.
The street illustrated above depicts a 120-foot roadway within a 150-foot right-of-way. PHOENIX, A Z
Light rail expansions should be coordinated with land use changes to promote devel opment of the corridor. 3
4 1
24
RECOMMENDATIONS
1 Construct green alleys with low-impact pavement materials, such as pervious pavements with high reflectivity to reduce heat island effects.
2 Alleys may be operated as pedestrian-only environments or as shared streets. Use bollards, signs, and design features that make clear the intended alley users.
Alley greening and maintenance may be initiated and carried out by local residents or neighborhood associations.2
3 To avoid puddling, stormwater run-off should be infiltrated in-place using permeable paving or rain gardens at the edge of the pedestrian path.3
4 To maintain a safe environ -ment, green alleys should have adequate lighting. Pedestrian-scale light fixtures that focus their illumination toward the ground and minimize light pollution are recommended. Public safety is of paramount consideration for all new and existing alleys. Good lighting is an essential prerequisite to a feeling of public safety in alleys.
5 Green alleys often run parallel to the larger street network, making them ideal low-speed, low-volume links for cyclists.
Alleys provide direct property access and eliminate the need for driveways along main roads where people are walking and biking. Consider the use of alleys in all new developments and renovations to existing properties.4
Green alleys may present certain unconventional maintenance respon sibilities. Use of textured pavements and other materials may be challenging to existing street sweepers and snowplows. Similar to shared streets, alleys may benefit from the application of snowplow compatible materials and provisions for maintenance equipment access.
DETROIT, MI
This alley in Detroit was transformed to manage stormwater using pervious pavement and native plants along the walkway.
The majority of residential alleys have low traffic and infrequent repaving cycles, resulting in back roads with potholes and puddling that are uninviting or unattractive. Green alleys use sustainable materials, pervious pavements, and effective drainage to create an inviting public space for people to walk, play, and interact.1
Green Alley
1 3
4
5
The alley shown above depicts a 14-foot path within a 28-foot right-of-way.
CO M M E R CI A L A L L E Y
Commercial alleys, though often thought of as dirty or unsafe, can be designed to play an integral role in a downtown street network and improve the pedestrian realm in and around commercial areas. The design of commercial alleys should strive to balance their necessary utilitarian features with their place-making potential.
1 Where access for vehicles is prohibited or minimal, commer- cial alleys may be constructed using low-impact pavement materials, such as pervious or modular paving.
2 Bicycle traffic may use commer-cial alleys. Similar regulations to those of shared space should apply.
Commercial alleys can be restricted for traffic during non-delivery hours for outdoor seating or other uses.
Where vehicle access is permitted, alleys should be maintained to allow easy access by trucks and other freight vehicles. Bollards and other street furniture should be designed to minimize conflicts with freight movements. In some cases, freight may be conveyed using hand trucks or small vehicles. In these cases, careful attention should be paid to the location of curbs and the access from loading zones to entrances to ensure smooth deliveries.
RECOMMENDATIONS
Intersections between alleys and side-walks have the potential to obstruct visibility for vehicles (if permitted) and passing pedestrians. Raise the intersection to the sidewalk grade and add rumble strips to mitigate these visibility issues. Warning signs should be provided to warn pedestrians of encroaching traffic.1
Freight may use green alleys for loading and unloading, which reduces double-parking on neighborhood
streets. SAN FRANCISCO, CA
Alley redesign can feature pavers for the traveled way, parking restrictions, and additional public space.
Commercial Alley
1
26
EXISTING CONDITIONS
The residential street in the illustration above is common in neighborhoods with low traffic volumes. Here, the configuration of the street network has formed a street segment that func tions naturally as a space for children to play and as a gathering place for residents.
Many low-volume residential streets in the United States were designed without sidewalks. Most of these streets have limited access and low volumes, allowing them to operate informally as shared spaces. Cities should aim to maintain low speeds and volumes on these streets, reinforcing their shared nature through materials and targeted design enhancements.
RECOMMENDATIONS
1 Textured or pervious pavements that are flush with the curb rein-force the pedestrian-priority nature of the street. Special pavements,
especially unit pavers, may be subject to additional maintenance costs and should be selected based on regional climate and long-term durability. Selection of snowplow-compatible materials is recommended for colder climates. Drainage channels should be provided either at the center of the street or along the flush curb, depending on underground utilities and other existing conditions.
2 Street furniture, including bollards, benches, planters, and bicycle parking, can help define a shared space, subtly delineating the traveled way from the pedestrian- only space.1
3 A shared street sign should be used at the entrance to a shared street. In some cases, a modified YIELD TO PEDESTRIANS sign (MUTCD 2B-2) may be added to reinforce the conversion in early stages.
Provide tactile warning strips at the entrance to all shared spaces. Warning strips should alert drivers and pedestrians.2
Low-volume residential streets, especially in older cities, often have narrow or crumbling sidewalks. Many of these streets operate as de facto shared spaces in which children play and people walk, sharing the roadway with drivers. Depending on their volume and role in the traffic network, these streets have the potential to be redesigned and enhanced as shared streets. Shared streets can meet the desires of adjacent residents and function foremost as a public space for recreation, socializing, and leisure.
Residential Shared Street
R E S I D E N T I A L S H A R E D S T R E E T
Depending on right-of-way, designers may consider providing a 3–5-foot clear path, protected from traffic. The clear path may be defined using planters, bollards, and street furniture, as well as detectable warning strips or textured pavers. For narrower shared streets and alleys, use of a clear path is discouraged.
The street illustrated above depicts a 20-foot
4 Shared streets generally permit motorists and bicyclists to operate in a 2-way fashion. Narrower shared streets may be made 1-way for motorists, though 2-way bicycle traffic should still be permitted. Certain restrictions and regulations may apply to vehicles on a shared street. Designers should strive to make these behaviors implicit through the design details of the street itself.
5 On wider shared streets,
staggered blocks of landscaping, head-in parking, back-in angled parking, or perpendicular parking can be used to create a chicane effect.3 In some cases, parking may be permitted directly adjacent to properties in a residential environment. Bollards, paving materials, and street furniture help to define parking spaces and to delineate private from public space.
Where necessary, traffic volumes can be decreased through network design and traffic calming as part of
VIC TORIA , BC, CANADA
Angled parking in alternating swaths curves the path of travel.
SANTA MONICA , CA
Signage reinforces the transition to a shared street.
1
2 3
4 5
28
Commercial shared streets differ from this earlier generation of pedestrian malls in both their regulation and implementation. Shared streets maintain access for vehicles operating at low speeds and are designed to permit easy loading and unloading for trucks at designated hours. They are designed to implicitly slow traffic speeds using pedestrian volumes, design, and other cues to slow or divert traffic.
EXISTING CONDITIONS
The street in the rendering above is a common sight in many older cities where downtown commercial streets may predate wider grid streets. In newer cities, a retail district with heavy parking utilization and narrow, congested sidewalks may have similar conditions or opportunities.
1 Sidewalk congestion creates unsafe conditions, as crowding forces some pedestrians to walk in the street to avoid crowds.
Vehicles in search of on-street parking create traffic congestion.
2 Loading and unloading trucks obstruct pedestrian and vehicle traffic. Truck drivers park on the side-walk to preserve vehicle flow while unloading, forcing pedestrians to mix with motorists.
RECOMMENDATIONS
3 Textured or pervious pavements that are flush with the curb reinforce the pedestrian-priority operation of the street and delineate a non-linear path of travel or narrow carriageway. Special pavements, especially unit pavers, may be subject to additional maintenance costs and should be selected based on regional climate and long-term durability. Selection of snowplow-compatible materials is recommended for colder climates. Drainage channels should be provided either at the center of the street or along the flush curb, depending on existing conditions and Many narrow or crowded
down-town streets operate informally as shared streets during rush hour or at lunchtime, but are not regulated as such. A commercial shared street environment should be considered in places where pedestrian activity is high and vehicle volumes are either low or discouraged. Commer-cial shared streets can be designed for narrow or wide cross sections, but become increasingly complex and difficult to maintain as a shared space as width increases.
From 1960–80, many neighborhood main streets and downtown
retail corridors were converted to pedestrian-only usage. These conversions were often
called “pedestrian malls.” In an era of declining downtown retail revenues due to competition from shopping center developments outside of historic cores, many of these conversions were unsuccessful or suffered from poor maintenance and a lack of programming or policing.1
Commercial Shared Street
1
2
CO M M E R CI A L S H A R E D S T R E E T
the overall street width. Drainage channels are often used to define the traveled way from the clear path.2
4 Commercial shared streets should be accessible by single-unit trucks making deliveries. Where commercial alleys are non-existent, it may be advantageous to design a shared street to accommodate large trucks, though significant changes to the design should be avoided. Designated loading and unloading zones may be defined through differences in pavement pattern or use of striping and signage.
5 Street furniture, including
bollards, benches, planters, street lights, sculptures, trees, and bicycle parking, may be sited to provide definition for a shared space, subtly delineating the traveled way from the pedestrian-exclusive area.
Shared streets may be closed to through traffic for specific portions of the day. Use movable planters and time-of-day restrictions to regulate the shared space.
Provide tactile warning strips at the entrance to all shared spaces. Warning strips should span the entire intersection crossing.
Prior to the application of a shared street, cities are encouraged to experiment with car-free hours or to test a conversion using temporary materials to evaluate the potential impact on traffic operations.
Commercial shared streets restrict transit access. For pedestrian streets that provide direct transit access, con-sider the application of a transit mall.3
Depending on the overall street width, designers may consider providing a 3–5-foot-clear path protected from traffic. The clear path should be defined using planters, bollards, and street furniture, as well as detectable warning strips or textured pavers. For narrower shared streets and alleys, use of a clear path is discouraged.
MONTREAL , CANADA
Shared streets should be designed so that people walk comfortably and naturally within the roadway.
3
4
5
CAMBRIDGE , MA
Street furniture helps define the shared space.
30
The City of Cambridge converted Harvard Square’s Winthrop Street into a shared street in 2007. This conversion was followed by the conversion of an alley, Palmer Street, into another shared corridor. Prior to their conversion, both streets were cramped and poorly maintained. Winthrop Street had narrow side-walks and uneven pavers that created an inhospitable environment for pedestrians. Both streets failed to meet accessibility standards of the Americans with Disabilities Act. With vehicle volumes under 1,000 ADT and high pedestrian traffic, the street already implicitly functioned as a shared street.
The city’s project formalized the shared operation of the corridor, while the reconstruction allowed for more efficient use of space on a small street and enabled the city to accommodate pedes-trians, bicyclists, outdoor diners, and motorists using a flush curb. Shared streets in Cambridge have transformed the public space, integrating and balancing commercial uses, streetperformers, restaurant activity, and trans-portation using an aesthetically pleasing design.
Interagency Coordination Multiple government departments worked collaboratively to realize Cambridge’s shared streets. The Community Development Department managed the design process and community involvement through a citizen advisory committee. Public Works reviewed the project design regarding long-term maintenance and accessibility issues. The Traffic, Parking, and Transportation Department oversaw traffic and parking regula tions, ensuring that deliveries were still feasible. Champions at the Harvard Square Business Association, the Harvard Square Design Committee, and the Historic Commission have
also contributed to the success of the shared streets. As part of these efforts, the city also created a new categorization for shared streets within their city code.
Maintenance
Both Winthrop and Palmer Street use standard color and interlocking concrete pavers, which facilitate easy maintenance. On Palmer Street, the use of in-ground lighting has proven more challenging to maintain. Similarly, bollards installed to protect buildings on Palmer Street have suffered wear and tear from truck traffic.
CAMBRIDGE SHARED STREETS
Street Design
Elements
The elements that make up city streets, from sidewalks to
travel lanes to transit stops, all vie for space within a limited
right-of-way. Transportation planners and engineers can
use this toolbox to optimize the benefits the community
receives from its streets.
33 Lane Width 37 Sidewalks
38 Sidewalk Zones 40 Sidewalk Design
45 Curb Extensions
47 Gateway 48 Pinchpoint 49 Chicane 50 Bus Bulbs
51 Vertical Speed Control Elements
53 Speed Hump 54 Speed Table 55 Speed Cushion
57 Transit Streets
58 Dedicated Curbside/ Offset Bus Lanes
60 Dedicated Median Bus Lanes 61 Contra-Flow Bus Lanes 62 Bus Stops
65 Stormwater Management
67 Bioswales
3 4
DISCUSSION
The relationship between lane widths and vehicle speed is complicated by many factors, including time of day, the amount of traffic present, and even the age of the driver. Narrower streets help promote slower driving speeds. which in turn reduce the severity of crashes. Narrower streets have other benefits as well, including reduced crossing distances, shorter signal cycles, less stormwater, and less construction material to build.
Lane widths of 10 feet are appropriate in urban areas and have a positive impact on a street’s safety without impacting traffic operations. For designated truck or transit routes, one travel lane of 11 feet may be used in each direction. In select cases, narrower travel lanes (9–9.5 feet) can be effective as through lanes in conjunction with a turn lane.2
RECOMMENDED
Lanes greater than 11 feet should not be used as they may cause unintended speeding and assume valuable right-of -way at the expense of other modes.
Restrictive policies that favor the use of wider travel lanes have no place in constrained urban settings, where every foot counts. Research has shown that narrower lane widths can effectively manage speeds without decreasing safety and that wider lanes do not correlate to safer streets.3 Moreover, wider travel lanes also increase exposure and crossing distance for pedestrians at inter-sections and midblock crossings.4
Use striping to channelize traffic, demarcate the road for other uses, and minimize lane width.
SAN FRANCISCO, CA
Striping should be used to delineate parking and curbside uses from the travel lane. Travel lanes are striped to define
the intended path of travel for vehicles along a corridor. Histor-ically, wider travel lanes (11–13 feet) have been favored to create a more forgiving buffer to drivers, especially in high-speed environments where narrow lanes may feel uncom-fortable or increase potential for side-swipe collisions.
Lane widths less than 12 feet have also historically been assumed to decrease traffic flow and capacity, a claim new research refutes.1
12' 12' 12' 12'
L A N E W ID T H
11' 10' 10' 8' 3' 6'
1 2
3
1 Lane width should be considered within the overall assemblage of the street. Travel lane widths of 10 feet generally provide adequate safety in urban settings while discour-aging speeding. Cities may choose to use 11-foot lanes on designated truck and bus routes (one 11-foot lane per direction) or adjacent to lanes in the opposing direction.
Additional lane width may also be necessary for receiving lanes at turning locations with tight curves, as vehicles take up more horizontal space at a curve than a straightaway.
Wide lanes and offsets to medians are not required but may be beneficial and necessary from a safety point of view.
OPTIONAL
2 Parking lane widths of 7–9 feet are generally recommended. Cities are encouraged to demarcate the parking lane to indicate to drivers how close they are to parked cars. In certain cases, especially where loading and double parking are present, wide parking lanes (up to 15 feet) may be used. Wide parking lanes can serve multiple functions, including as indus-trial loading zones or as an interim space for bicyclists.
3 For multilane roadways where transit or freight vehicles are present and require a wider travel lane, the wider lane should be the outside lane (curbside or next to parking). Inside lanes should continue to be designed at the minimum possible width. Major truck or transit routes through urban areas may require the use of wider lane widths.
2-way streets with low or medium volumes of traffic may benefit from the use of a dashed center line with narrow lane widths or no center line at all. In such instances, a city may be able to allocate additional right-of-way to bicyclists or pedestrians, while permitting motorists to cross the center of the roadway when passing. Redesign
36
8
5
th
Percentile
S
p
e
e
d
(
m
p
h
c
o
nve
rt
e
d
from
km/hr
)
31.1 62.1
40.4
37.3
9'10" 10'8" 11'6" 12'4"
59.0
55.9
52.8
46.6 49.7
43.5
Average Lane Width (feet converted from meters)
13'2" 13'11"
34.2
Wider travel lanes are correlated with higher vehicle speeds.
85th Percentile Speed of Traffic Regression Line
“As the width of the lane increased, the speed on the roadway increased... When lane widths are 1 m (3.3 ft) greater, speeds are predicted to be 15 km/h (9.4 mph) faster.”
Chart source: Fitzpatrick, Kay, Paul Carlson, Marcus Brewer, and Mark Wooldridge. 2000. “Design Factors That Affect Driver Speed on Suburban Streets.”
Sidewalks
Sidewalks play a vital role in city life. As conduits for
pedestrian movement and access, they enhance
connectivity and promote walking. As public spaces,
sidewalks serve as the front steps to the city, activating
streets socially and economically. Safe, accessible,
and well-maintained sidewalks are a fundamental and
necessary investment for cities, and have been found to
enhance general public health and maximize social capital.
Just as roadway expansions and improvements have
3 8
Prevailing design guidelines recommend a minimum sidewalk cross-section of 5 feet, exclusive of other amenities and large enough for two people walking side by side. While this dimension meets minimum ADA accessibility stan-dards, many cities have chosen to adopt wider standards. Sidewalk standards should accommodate higher anticipated pedestrian volumes and provide ample space for an expanded frontage zone as well as other street furniture, such as trash receptacles, bus stops, signage, and bike share stations.1
1
FRONTAGE ZONEThe frontage zone describes the section of the sidewalk that func-tions as an extension of the building, whether through entryways and doors or sidewalk cafes and sandwich boards. The frontage zone consists of both the structure and the façade of the building fronting the street, as well as the space immediately adjacent to the building.
2
PEDESTRIANTHROUGH ZONE
The pedestrian through zone is the primary, accessible pathway that runs parallel to the street. The through zone ensures that pedestrians have a safe and adequate place to walk and should be 5–7 feet wide in residential settings and 8–12 feet wide in down-town or commercial areas.
Frontage Zone Pedestrian
Through Zone
SID E WA L K ZO N E S
3
STREET FURNITURE/CURB ZONE
The street furniture zone is defined as the section of the sidewalk between the curb and the through zone in which street furniture and amenities, such as lighting, benches, newspaper kiosks, utility poles, tree pits, and bicycle parking are provided. The street furniture zone may also consist of green infrastructure elements, such as rain gardens or flow-through planters.
4
ENHANCEMENT/BUFFER ZONE
The enhancement/buffer zone is the space immediately next to the sidewalk that may consist of a variety of different elements. These include curb extensions, parklets, stormwater management features, parking, bike racks, bike share stations, and curbside bike lanes or cycle tracks.
Street Furniture/ Curb Zone
40
CRITICAL
Sidewalks have a desired minimum through zone of 6 feet and an absolute minimum of 5 feet.Where a side walk is directly adjacent to moving traffic, the desired minimum is 8 feet, providing a minimum 2-foot buffer for street furniture and utilities.6
Sidewalk design should go beyond the bare minimums in both width and amenities. Pedestrians and businesses thrive where sidewalks have been designed at an appropriate scale, with sufficient lighting, shade, and street-level activity. These considerations are especially important for streets with higher traffic speeds and volumes, where pedestrians may otherwise feel unsafe and avoid walking.
Sidewalks should be provided on both sides of all streets in all urban areas. On shared streets, the street itself serves as the path of travel and should be designed in accordance
with accessibility recommendations outlined in the shared street section of these guidelines. In certain instances, such as on more rural or suburban roads connecting urban areas, it may be advantageous to build a shared-use path adjacent to the main roadway as a substitute for a sidewalk. In this case, the shared use path should meet the general criteria to serve adequately as a sidewalk or pathway.
DISCUSSION
Sidewalks are an essential component of the urban environment and serve as key corridors for people, goods, and commerce. In accordance with ADA accessibility guidelines, sidewalks should be provided on all streets in urban areas.3
Numerous studies have shown that good pedestrian network connectivity and walkability have a positive impact on land values.4
Sidewalks have significant lifespans and can be maintained without replacement for 25 years or more, depending on the context.5
PHILADELPHIA , PA
The sidewalk on Walnut Street over the Schuylkill River was widened from 8 to 12 feet to provide a wider buffer with lighting. The sidewalk is the area where
people interface with one another and with businesses most directly in an urban environment. Designs that create a high-quality experience at street level will enhance the economic strength of commercial districts and the quality of life of neighborhoods.2
